Biology Reference
In-Depth Information
Keywords Dairy cow • Dry period • IGF-I • NEFA • Ovarian activity
Abbreviations
CP Crude protein
dm Dry matter
EE Ether extract
IGF-I Insulin-like growth factor I
NDF Neutral detergent fiber
NEFA Non-esterified fatty acids
NFC
Non fiber carbohydrate
4.1
Introduction
The choice of dry period length in dairy cows is mainly based on expectations of
milk production; however, the effects on health and postpartum (PP) reproductive
efficiency should not be underestimated. It is well known that the duration of dry
periods has an influence on energy balance, which in turn affects reproductive
efficiency (Watters et al. 2009 ). The first PP ovulation occurs 10-14 days after the
energy balance has reached its nadir. Some authors (Rastani et al. 2005 ) have
suggested that the reduction or the absence of a dry period results in a less-
pronounced negative energy balance than does a traditional dry period.
Studies on the effects of a short dry period on PP reproductive performance have
produced differing results (Gumen and Wiltbank 2005 ; Pezeshki et al. 2007 ). This
study considers the impact of a short dry period on the PP resumption of ovarian
cyclicity and on the energy balance in dairy cows by assessing NEFA and IGF-I
plasma concentrations.
4.2 Materials and Methods
Twenty-five pregnant Friesian cows of second and third parity were divided into
two groups (C, n
13) according to parity and lactation performance
during the previous year (C: 25.5 kg/day, 3.6% fat, 3.3% protein, T: 26.5 kg/day,
3.6% fat, 3.15% protein). The dry period lasted traditionally (9 weeks) for group C
and was short (5 weeks) for group T. Both experimental groups were fed the same
ration (CP
12; T, n
¼
¼
32.1%
dm) containing: corn silage (40%), alfalfa hay (14.5%), alfalfa meal (14%), and
17.9% dm, EE
3.2% dm, NDF
41.3% dm, and NFC
¼
¼
¼
¼
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